The overall goal of this research proposal is to gain an understanding of the role of the second messenger inositol l,4,5-trisphosphate (IP3) in olfactory transduction. Work in our laboratory has concentrated on two model systems the channel catfish and the rat. In these systems some odorants transiently increase intracellular levels of IP3. Experimental results suggest that lP3 binds to a unique ciliary IP3 receptor/channel resulting in membrane depolarization. We will apply the complementary approaches of biochemistry and molecular biology to definitively identify the olfactory IP3 receptor (IP3R) through purification of the receptor protein and isolation of the cDNA that encodes for the receptor from a rat olfactory cDNA library. Both the receptor protein and the cDNA clone will be sequenced and characterized. The cDNA will be expressed in a cell line and the expressed protein characterized using a multidisciplinary approach. The results of biochemical studies such as filtration binding, gel electrophoresis and photoaffinity labelling will be compared for native and expressed proteins. Additionally, electrophysiological studies will determine the properties of the receptor/channel in isolated inside- out patches from cells containing expressed receptor and compared to these properties from isolated cilia patches. Antibodies and riboprobes to sequences unique to the olfactory IP3 receptor will be prepared and used to study tissue specificity and examine biochemical and functional properties of the receptor protein. The results of these studies should permit the definitive identification of an olfactory-specific IP3 receptor protein.